In a gasifier which produces combustible gas by thermally decomposing carbonaceous feedstock such as coal, biomass fuel such as a wood pellet, or petroleum coke, ashes of the carbonaceous feedstock melt and accumulate as slag in a slag bath provided at a bottom portion of the gasifier. Slag cooling water is stored in the slag bath, and the slag falls into the slag cooling water, thereby being rapidly cooled and solidified, and is crushed.
The slag solidified and crushed in this manner and collected in the slag bath is discharged to the outside of the system of the gasifier via a lock hopper provided outside the gasifier. The slag has higher density than the slag cooling water, and therefore, in the related art, when the slag is moved from the slag bath to the lock hopper, the slag naturally drops due to gravity. For example, PTL 1 discloses a slag discharge system in which a lock hopper is disposed below a gasifier.
However, according to the slag discharge system described above, in order to provide the lock hopper below the gasifier, the disposition position of the gasifier becomes higher. Therefore, the height from the installation surface of a plant to an upper part of the gasifier is increased. The disposition position of the gasifier becomes higher, so that the disposition positions of a support frame supporting the gasifier, an operation table, or the like become higher.
Therefore, a slag discharge system as disclosed in PTL 2 has been proposed. In this slag discharges system, a lock hopper is disposed by the side of a gasifier, a slag discharge line communicating with the lock hopper is provided from a slag bath of a bottom portion of the gasifier, a water stream from the slag bath to the lock hopper is formed in the slag discharge line by a circulation pump, and slag in the slag bath is discharged to the lock hopper by this water stream.
In this way, the slag can be transferred from the slag bath to the lock hopper by being carried by a flow of slag cooling water, and therefore, the lock hopper can be disposed by the side of the gasifier, so that the height from the installation surface of a plant to an upper part of the gasifier can be reduced.